Microprocessor-controlled motor systems are vulnerable to electrical noise on the input leads to the microprocessor, which noise can sometimes make the microprocessor "hang" and thereby bring the motor itself to a standstill. This can occur, for example, through bursts of transient impulses or Electro-Static Discharge ("ESD"), i.e., noise signals which may arise in environments filled with strong electrical activity.
One generally tries to alleviate this situation by providing protective circuitry at the inputs of such a microprocessor, but this is costly and doesn't always achieve the desired result.